The present invention relates to a technical field of a pressure intensifying master cylinder in which master cylinder pressure is intensified with fluid pressure regulated according to the input force applied through an operating means and, more particularly, to a technical field of a pressure intensifying master cylinder in which the input side and the output side are separately operated so that the input travel can be set freely without the influence of operation of the output side. In the following description, the term xe2x80x9cmaster cylinderxe2x80x9d will be sometimes referred to as xe2x80x9cMCYxe2x80x9d.
For example, in a conventional brake system of an automobile, a braking pressure intensifying device has been employed which hydraulically intensifies the pedal force on a brake pedal into predetermined magnitude to develop large braking pressure. The braking pressure intensifying device functions to provide large braking force from small pedal force on the brake pedal, thereby securing the braking performance and reducing the fatigue of a driver.
In the conventional braking pressure intensifying devices, a control valve is actuated by an input based on the pedal force applied to the brake pedal to develop hydraulic fluid pressure according to the input and the developed hydraulic fluid pressure is introduced into a power chamber, thereby intensifying the input at a predetermined ratio to output intensified pressure. A piston of a master cylinder is moved by the output of the braking pressure intensifying device so that the master cylinder outputs master cylinder pressure. The master cylinder pressure is introduced as braking pressure into wheel cylinders, thereby actuating the wheel brakes.
By the way, conventional brake systems employ various brake controls such as for controlling the braking force in a brake maneuver, for example, Anti-Lock Control (ABS), Brake Assist Control for assisting pedal force in the event of emergency braking, and Regenerative Brake Coordination Control for controlling the braking pressure produced by a service brake system when a regenerative brake system is used to develop braking pressure during the braking by the service brake system, and automatic brake controls, for example, a brake control for controlling the distance from another vehicle, a brake control for avoiding a collision with an obstacle object, and Traction Control (TRC).
Most of such brake controls are normally conducted in a brake circuit between the master cylinder and the wheel cylinders. However, when the brake control is conducted in the brake circuit after the master cylinder, it is required to prevent the input travel of the braking pressure intensifying device from being influenced by such brake controls, for instance, for obtaining better operational feel.
However, in a brake system in which a conventional braking pressure intensifying device and a brake master cylinder are combined, the travel of a piston of the master cylinder is fixed by the relation between the master cylinder and wheel cylinders. The travel of an input shaft of the braking pressure intensifying device i.e. the pedal travel of a brake pedal, depends on the travel of the piston of the master cylinder. Consequently, the travel of input side is influenced by the brake controls conducted in the brake circuit after the master cylinder. In the combination between the conventional braking pressure intensifying device and the brake master cylinder, it is difficult to securely and sufficiently satisfy the aforementioned requirement.
For changing the travel characteristic of the brake pedal as the input side to obtain better operational feel, the brake master cylinder and the brake circuit after the brake master cylinder are also influenced so that some change on the output side, for instance a size change on the master cylinder, should be required. By the change on the output side, the output characteristic of the brake system is influenced. This means that the overall change on the brake system is required, i.e. large-scale change is required.
It is further desired that the input side is influenced as little as possible by brake circuit which may differ according to the type or size of vehicle.
If the input side and the output side are just separated from each other to produce outputs regardless of the travel of the input side, the input side does not travel so that the travel of the input side can not be ensured.
For this, it has been conventionally proposed that a travel simulator is provided on the brake circuit after the master cylinder to prevent the travel of the input side from being influenced by the brake control after the master cylinder and to ensure the travel of the input side.
However, to add specially the travel simulator, many parts such as a travel cylinder and an electromagnetic shut-off valve used for the travel simulator are required, making the structure complex and increasing the cost.
There is still a problem that brakes must be securely operated in case of a fluid pressure source failure even with a travel simulator.
In an anti-lock control system, it is desired that when one or more braked wheels are in locking tendency, the braking force is controlled to cancel the locking tendency of the wheels. Further, in a regenerative coordination brake system, when the regenerative brake system is operated during the operation of the braking pressure intensifying device, the braking force produced by the braking pressure intensifying device should be reduced by an amount corresponding to the braking force produced by the regenerative brake system. In this case, it is desired to reduce the output of the braking pressure intensifying device to a value obtained by subtracting the output of the regenerative brake system from the output of the braking pressure intensifying device. In a brake system composed of a combination of a service brake system and a brake assist system, it is desired to increase the output of the braking pressure intensifying device to intensify the braking force produced by the braking pressure intensifying device in such case that brake assist operation is needed, for example, a case that a driver can not depress a brake pedal enough during the operation of the braking pressure intensifying device so as not to develop predetermined braking force.
When the brake control is performed in a brake maneuver just like the above case, the brake pedal is not influenced even with the travel simulator.
Further, in a brake system for controlling the distance from a front vehicle, it is desired to hold the distance constant by automatically actuating wheel brakes when the distance becomes short during running. In a brake system for avoiding a collision, it is desired to avoid a collision with an obstacle object by automatically actuating wheel brakes when there is a possibility of collision with the obstacle object. Furthermore, in a traction control system, it is desired to cancel a slipping tendency to ensure the secure starting by automatically actuating the brakes of the driving wheels when the driving wheel(s) is in slipping tendency at the starting.
As mentioned above, it is desired that the brake pedal is not influenced when the automatic braking is conducted even with the travel simulator.
Further, it is desired that such a system for controlling the braking force during braking operation or controlling the automatic braking can be manufactured with a simple structure.
Moreover, it is desired that the input-travel characteristic, the input-braking pressure characteristic, or the travel-braking pressure characteristic is allowed to be changed according to the condition of a vehicle or the like, with the structure remaining simple.
It is an object of the present invention to provide a braking pressure intensifying master cylinder of which the travel characteristic at the input side can be freely changed without the influence of the output side.
It is another object of the present invention to provide a braking pressure intensifying master cylinder with simple structure which can intensify master cylinder pressure to obtain large braking force when necessary.
It is still another object of the present invention to provide a braking pressure intensifying master cylinder which can securely operate even in case of the fluid pressure source failure, and which can be manufactured to be compact at a low cost.
To achieve the aforementioned objects, the present invention provides a braking pressure intensifying master cylinder comprising at least: an input shaft which travels by input applied in braking maneuver; a control valve of which operation is controlled by said input shaft to regulate the fluid pressure of the fluid pressure source to develop fluid pressure corresponding to said input; a pressurized chamber into which the fluid pressure regulated by said control valve is supplied; and a master cylinder piston which is actuated by the fluid pressure supplied into the pressurized chamber to develop master cylinder pressure, wherein said control valve is biased by biasing force of a biasing means in a direction opposite to the operational direction of said input shaft and is biased by the fluid pressure regulated by said control valve in the operational direction of said input shaft, and said input shaft travels such that the force produced by the fluid pressure regulated by said control valve and the biasing force of said biasing means are balanced.
The braking pressure intensifying master cylinder of the present invention is characterized by further comprising a reaction chamber which can communicate with said pressurized chamber and into which the fluid pressure regulated by said control valve can be supplied, wherein the fluid pressure supplied in said reaction chamber acts on said input shaft against said input.
The braking pressure intensifying master cylinder of the present invention is also characterized in that said control valve has a valve spool which is slidably disposed to develop said regulated fluid pressure, and said valve spool is biased by the operational force produced by the fluid pressure regulated by said control valve and by the biasing force of said biasing means in directions opposite to each other.
The braking pressure intensifying master cylinder of the present invention is also characterized in that said control valve comprises said valve spool and said input shaft, said valve spool travels such that said biasing force and said operational force are balanced, and said input shaft travels depending on the travel of said valve spool.
The braking pressure intensifying master cylinder of the present invention is also characterized in that said control valve comprises said valve spool and said housing and said input shaft travels such that said biasing force and said operational force which bias said valve spool are balanced.
The braking pressure intensifying master cylinder of the present invention is also characterized by further comprising an electromagnetic shut-off valve for controlling the communication/isolation between said fluid pressure source and said pressurized chamber, an electromagnetic selector valve to be selectively controlled for allowing the communication between said pressurized chamber and said reaction chamber or restricting the communication therebetween by a relieve valve, and a controller for controlling the opening/closing of said electromagnetic shut-off valve and the selection of said electromagnetic selector valve.
The braking pressure intensifying master cylinder of the present invention is also characterized by further comprising a first electromagnetic shut-off valve for controlling the communication/isolation between said fluid pressure source and said pressurized chamber, a second electromagnetic shut-off valve for controlling the communication/isolation between said fluid pressure source and said reaction chamber, and a controller for controlling the opening/closing of said first and second electromagnetic shut-off valves.
The braking pressure intensifying master cylinder of the present invention is also characterized in that said fluid pressure source comprises a pump which is actuated when necessary to discharge hydraulic fluid, and an accumulator in which pressure exceeding a setting value is stored by said pump, and that said first electromagnetic shut-off valve controls the communication/isolation between said pump and said pressurized chamber, and said second electromagnetic shut-off valve controls the communication/isolation between said pump and said reaction chamber, and the communication/isolation between said accumulator and said pressurized chamber is controlled by a third electromagnetic shut-off valve of which opening/closing is controlled by said controller.
The braking pressure intensifying master cylinder of the present invention is also characterized by further comprising an electromagnetic shut-off valve for controlling the communication/isolation between said fluid pressure source and said pressurized chamber, and a controller for controlling the opening/closing of said electromagnetic shut-off valve.
The braking pressure intensifying master cylinder of the present invention is also characterized in that said fluid pressure source comprises at least an accumulator in which pressure exceeding a setting value is stored and is characterized by further comprises: a first electromagnetic shut-off valve for controlling the communication/isolation between said accumulator and said pressurized chamber, a second electromagnetic shutoff valve for controlling the communication/isolation between said pressurized chamber and said reaction chamber, and a controller for controlling the opening/closing of said first and second electromagnetic shut-off valves.
The braking pressure intensifying master cylinder of the present invention is also characterized in that said master cylinder piston is pressed by said input shaft to develop master cylinder pressure when no fluid pressure is developed in said pressurized chamber due to failure of said fluid pressure source even with travel of said input shaft in a braking maneuver.
According to the braking pressure intensifying MCY of the present invention having the aforementioned construction, the pressure intensifying function is contained in the MCY itself, thus eliminating the need for a booster such as a vacuum booster or a hydraulic booster as conventionally used. Therefore, the entire length of the braking pressure intensifying MCY can be shorter than the length of a combination of a MCY and a booster as the conventional one because of no booster. This also enables to facilitate the structure of the brake system and improve the flexibility for installation of the braking pressure intensifying MCY.
The input shaft and the master cylinder piston can be operated separately from each other when operated and the input shaft travels such that the fluid pressure regulated by the control valve and the biasing force of the biasing means are balanced so that the control valve can function as a travel simulator.
The pressurized chamber and the reaction chamber can be isolated from each other, whereby fluid pressure of the fluid pressure source can be supplied to the pressurized chamber independently from the reaction chamber. This enables the regenerative brake coordination control, the automatic brake control, the auto cruise compensation control, and/or the brake assist control.
The control valve has a valve spool and the input shaft travels such that the operational force produced by the fluid pressure regulated by the control valve and the biasing force of the biasing means are balanced, whereby the valve spool can function as a travel simulator.
By changing the pressure receiving area of the control valve on which fluid pressure regulated by the control valve acts and/or changing the biasing force of the biasing means, the travel characteristic of the input shaft as the input side can be freely changed independently from the output side, without influence on the master cylinder pressure as the output side of the braking pressure intensifying MCY.
Because the travel characteristic of the input shaft is not influenced by the master cylinder pressure, the operational feel is improved.
The travel simulator is built in the braking pressure intensifying master cylinder, that is, no external simulator is necessary, thereby allowing compact design of the braking pressure intensifying MCY.
When the electromagnetic selector valve is selected in the pressure-regulating position by the controller, the fluid pressure of the reaction chamber should be lower than the fluid pressure of the pressurized chamber by an amount corresponding to the relief pressure of the relief valve, whereby the braking pressure intensifying MCY can exhibit jumping characteristic.
The braking pressure intensifying MCY of the present invention may be applied to an open-center type MCY. In this case, when a predetermined period of time has passed after the input shaft starts to travel in a braking maneuver, the controller opens the second electromagnetic shut-off valve, whereby the braking pressure intensifying MCY can exhibit jumping characteristic.
The controller controls the opening/closing of the first and second electromagnetic shut-off valves based on information indicating operational condition of regenerative braking, whereby the braking pressure intensifying MCY is operated to coordinate the operation of the regenerative braking so as to obtain optimal braking force as a whole corresponding to the braking force generated by the regenerative braking.
Further, the controller controls the opening/closing of the first through third electromagnetic shut-off valves based on information for actuating automatic braking, information for controlling the operation of the braking for holding the vehicle to run at a constant speed, and/or information for controlling the braking for brake assist, whereby the braking pressure intensifying MCY is operated to conduct the automatic brake control, the auto cruise compensation control, and/or the brake assist control.
The braking pressure intensifying MCY of the present invention may be applied to a closed-center type MCY. When a predetermined period of time has passed after the input shaft starts to travel in a braking maneuver, the controller opens the second electromagnetic shut-off valve, whereby the braking pressure intensifying MCY can exhibit jumping characteristic. The controller controls the opening/closing of the first electromagnetic shut-off valve and the second electromagnetic shut-off valve based on information indicating operational condition of regenerative braking, information for actuating automatic braking, information for controlling the operation of the braking for holding the vehicle to run at a constant speed, and/or information for controlling the braking for brake assist, whereby the braking pressure intensifying MCY is operated to conduct the regenerative brake coordination control, the automatic brake control, the auto cruise compensation control, and/or the brake assist control.
According to the present invention, the master cylinder piston can be directly operated by the input of the input shaft when no fluid pressure is developed in the pressurized chamber due to the failure of the fluid pressure source. Therefore, the wheel brakes can be securely actuated whenever no fluid pressure is developed in the pressurized chamber due to the failure of fluid pressure source.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.